1. Field of the Invention
The present invention relates generally to lighting systems utilizing a high intensity light source, and more particularly to a more durable and higher efficiency lighting system including a high intensity light source and a plastic fiber optic cable bundle for transmitting the light to a remote area.
2. Description of the Related Art
Lighting systems are known in the art that utilize a high intensity light source which generates an enormous amount of radiant energy. The light energy is transmitted through optical fibers of the bundle to the other terminal end of the bundle and dissipated to the desired locations or areas to be illuminated. The terminal end adjacent the light source or the source end of the cable bundle is exposed to a large amount of radiant energy that is in converted to heat if absorbed by the components. The amount of heat absorbed in a typical remote lighting system can increase the temperature of the source end or bundle tip to well over a 100.degree. C.
The typical glass fiber bundle construction at least at the source end includes a plurality of optical fibers bound together. Each of the fibers has a round or circular cross section so when they are bound or packed together, they define spaces between the individual fibers. The spaces are filled with an adhesive resin material in order to securely hold or bond the fiber ends to one another. A metal ferrule or ring holds the fibers in place as well, thus forming a terminal end of the cable. The adhesive resin material is not optically transparent and thus light energy hitting the resin and not the optical fiber tips is absorbed by the resin material and not transmitted through the fibers. This reduces the transmission efficiency of the bundle. Additionally, the absorbed heat can damage or destroy the terminal ends of the bundle. The metal ferrule also absorbs and retains heat to further exacerbate the problem.
Heat absorbed by the terminal end destroys or melts the resin at the tip of the fiber optic bundle. As the resin material softens, the resin can loosen from within the spaces between the fibers. The loosened resin results in separation of the fiber ends from one another which affects the light transmission efficiency and quality of the bundle. The loosened resin also blocks some of the light from entering the fiber optic cables. Therefore, more light energy is absorbed at the tip of the fiber optic bundle, further decreasing the efficiency of the lighting system.
Such remote high intensity lighting systems utilize glass optical fibers that inherently have relatively high melting temperatures. However, plastic fibers are more desirable because of higher flexibility, lower weight and a much lower cost. A problem with plastic fibers is that they have a relatively low melting temperature, around 70.degree. C. in high transparency fibers. Thus only low concentrations of light energy can be used along with plastic cables to avoid melting or destroying the fibers, eliminating many of the benefits of the plastic fibers.
Attempts have been made to reduce temperatures of the fiber end adjacent the light source by designing special cooling systems to dissipate heat generated by the high intensity light source. These methods and systems for cooling fiber optic cable bundles are relatively expensive to use and have not been found to be successful in reducing temperatures below the melting point of plastic optical fibers.
One such system or method is disclosed in the U.S. Pat. No. 5,479,322 issued to Kacheria. Air is moved through an enclosure by a fan and is directed via a baffle system toward the end of the fiber optic bundle. The air is moved essentially parallel relative to the fiber optic bundle and therefore does not directly contact the tip of the fiber optic bundle. The cooling is thus provided by air passing into the primary chamber of the enclosure which houses the high intensity light source and then out of the enclosure in order to carry away some of the heat. However, this system does not effectively dissipate heat absorbed by the optical fibers at the terminal end or bundle tip, because the plenum is created inside of the housing that includes the heat sources and because air flow does not run across the bundle directly.
Another such system is disclosed in U.S. Pat. No. 4,825,341 issued to Awai. The system disclosed by Awai also utilizes air moving through an enclosure in order to dissipate the heat generated by the high intensity light source. This particular system utilizes a downstream fan to draw air through the enclosure from behind the light source. Air is drawn from an intake through a plurality of entrance ducts or passages into the enclosure containing both the light source and the fiber optic bundle tip. The fiber optic bundle tip includes a bezel block extending into the chamber containing the high intensity light source. This type of system utilizes a high volume of air in order to dissipate the heat generated by the light source within the chamber. However, heat absorbed by the fiber optic bundle and the bezel block that surrounds the bundle tip is not efficiently dissipated. Additionally, the bezel block may actually assist to retain heat around the bundle tip.
Another method is disclosed in U.S. Pat. No. 5,653,519, issued to Dobbs. The system disclosed in Dobbs also does not efficiently cool the tip of the fiber optic bundle. Again, air is merely passed through the chamber in order to remove heated air within the chamber to dissipate the heat collected therein. Any heat absorbed by the fiber optic bundle is essentially retained within the bundle tip and therefore the problems discussed above are again not solved by the disclosure of Dobbs.
An additional system is disclosed in U.S. Pat. No. 5,099,399, issued to Miller et al. which discloses surrounding part of the terminal end of the fiber optic cable with a heat sink or bushing. The heat sink has an air opening or passage adjacent and parallel to the fiber optic bundle in order to pass air through the heat sink into the housing which encloses the high intensity light source. Air is drawn through the passages of the heat sink by a fan located downstream of the light source within the housing. A glass rod is placed concentrically abutting the end of the plastic fiber optic bundle and protrudes into the housing and is closely adjacent the high intensity light source.
The system disclosed by Miller et al. again dissipates heat from within the housing by moving air therethrough. The system also will dissipate some heat from the end of the plastic fiber optic bundle. However, because one end of the glass rod touches the tip of the fiber optic bundle and the exposed end of the glass rod faces the high intensity light source, light energy conducted through the glass rod has high light density so that the amount of heat absorbed by bundle components cannot be reduced sufficiently. The heat sink and also the air passages do not provide direct cooling of the fiber optic bundle tip, but instead only of the glass rod. Additionally, the light energy is transmitted through the glass rod to the plastic bundle and thus generates heat based upon the amount of radiant energy absorbed in the rod. The heat generated within the glass rod is transmitted directly to the bundle tip at the contact point between the plastic and the glass. The plastic bundle has a very low thermal conductivity and without special cooling of the tip of the bundle itself, heat at its very tip is generated and is not adequately cooled by the disclosure of Miller et al.
At the remote or distal end of the fiber optic bundle of remote lighting systems, light emanating through the fiber optic cables is transmitted to the desired locations or areas. Glass optical fibers having diameters in a range of about 30 to about 100 microns have been known and used for several decades. The optical fibers are assembled together parallel to one another with the ends of each fiber terminating in a surface finished end having a mirror quality finish at each end of the bundle.
For glass optical fibers, the typical method utilized for preparing and surfacing the fiber optic bundle ends includes the following steps. Each end portion of the bundled grouping of raw fibers is dipped in a liquid, preferably alcohol to create Vander-Wals forces that bond and compress the fibers together and to align the fibers in a parallel fashion by means of combing. The fibers are combed to align them in a parallel manner and then further compressed by means of a wrap-around cord wound around each end of the bundle. The ends of the bundle are pulled through a cylindrical metal ferrule to tightly pack the fibers together. The fibers are then dried to evaporate the liquid or alcohol. A bonding agent epoxy resin is then applied to the ends to fill the spaces between the individual optical fibers of the cable and to securely hold the fibers in place.
After curing of the resin is complete, the excessive fibers and resin epoxy extending beyond the end of the metal ferrule is cut off or removed. Both ends or tips of the fiber optic cable bundle are then surface polished in order to form a mirror quality surface of each terminal end of the cable.
One critical element in the construction of fiber optic cables is defined as the packing factor or ratio of the cross-section of the actual fiber material to the cross-section of the internal area of the terminating metal ferrule and epoxy resin. The packing factor determines at least partially the loss of light due to absorption of light energy in the space between the fibers containing the adhesive or resin material. The typical packing factor for conventional glass optical fiber bundles is about 65-70 percent wherein the glass optical fibers are on the order of 50 microns in diameter. This means that about 30-35 percent of the terminal end transverse face is ferrule or epoxy resin material. The metal ferrule material and resin are not light transparent and therefore absorb any light energy incident thereon, thus further reducing the efficiency of the bundle.
An additional problem is that for fiber optic remote lighting systems, the light source is an extremely high intensity lamp producing an enormous amount of radiant energy, especially for sources such as xenon and metal-halide lamps combined with an elliptical reflector. The luminous flux produced by the light sources is transmitted by the fibers and absorbed by the metal ferrule and the resin material between the fibers. The heat absorbed by the terminal end greatly increases the temperature of the tips of the fiber optic bundle.
The temperature at the input or source end of the cable can reach well over 100.degree. C. and destroy the resin at the tip of the bundle by burning it or softening it so that it comes out of the space between the fibers. The loosened resin material can block the light path through the fibers. As described above, attempts have been made to utilize volume air movement to generally dissipate heat within a chamber or enclosure of the apparatus.
Plastic light guides utilizing plastic fiber optic elements are desirable because of the low cost, low weight, high flexibility and larger cable diameters. However, one disadvantage is that the plastic optical fibers have melting temperatures as low as 70.degree. C. These low melting temperatures result in destruction of the optical fibers and terminal ends when exposed to the high intensity light sources in remote lighting systems. The high heat absorption can also destroy the cables downstream of the terminal ends. The glass fiber cable construction at the terminal ends is inadequate for use with plastic optical fibers in high concentration light energy systems.
An ideal highly efficient lighting system would include a high intensity light source coupled to a large diameter plastic fiber optic cable bundle. However, as described above it is heretofore not possible to utilize a high intensity light source coupled to the plastic optical fibers. This is because there is currently no means by which the terminal end of the bundle can be manufactured so as not to absorb large amounts of light energy as heat. This is further because all of the known cooling methods are not efficient enough in order to continually maintain a temperature at the terminal end of the cable below the melting point of plastic optical fibers which is about 70.degree. C.